The present invention relates generally to apparatus used to dispense a plurality of liquids through a single orifice, and more particularly it relates to an insert used in a polyurethane foam dispenser to separate the plural polyurethane foam mix components from each other in the dispenser and to permit water flushing to occur to obtain a foam dispenser that may be utilized without the need for solvent cleaning.
Polyurethane foams are formed by the reaction of an isocyanate component and hydroxyl-bearing compounds. When mixed in the presence of a catalyst, a surfactant, and a blowing agent, these chemicals react to form cellular cross-linked polymer chains, more commonly known as a polyurethane foam. Each of these components of the plural component material, by itself, is generally stable. Thus, each component will not cure or cross-link for extended periods of time, often as long as several months, if they are properly stored. However, when the isocyanate component and the polyol component, a preformulated compound that includes a surfactant, a catalyst and a blowing agent, are mixed together in proper proportions, an exothermic chemical reaction of the isocyanate and polyol occurs. This reaction causes a continued expansion that is evidence of the polymerization and manifests itself as foam which cross-links and cures. The cross-linking and curing usually is substantially completed in a matter of seconds.
Polyurethane foam dispensers are well known and have achieved a high degree of usage in insulating or packaging applications. Their use is particularly widespread in the boat manufacturing industry, where foam is used to enhance the buoyancy of the watercraft and in the refrigeration industry, where foam is used to insulate cooling compartments such as refrigerators, freezers and large refrigerated railroad tank cars or highway trucks. This type of a manufacturing application requires a low density foam that can be dispensed by apparatus. One of the problems with foam dispensing equipment used in the marine and refrigeration industries involves the need to obtain a fully expanded low density foam that does not readily cure within the dispenser or after curing require solvent cleaning. This latter consideration is becoming a more compelling need because of the hazardous chemicals employed as solvents, concern with environmental pollution and imminent strict governmental regulations in this area.
Prior foam dispensing apparatus has employed either an air purging, solvent purging or flushing, mechanical purging such as with a rod optionally fitted with a surrounding scraper, or a combination of these approaches in order to obtain plural component foam dispensing apparatus with sufficiently long operating times before requiring cleaning or replacement of internally clogged components. Typical examples of devices utilizing such systems include those disclosed in U.S. Pat. Nos. 3,263,928; 4,377,256; 4,469,251; 4,534,802; 4,568,003 and 4,867,346. However, these devices do not always yield the desired length of operating time without internal clogging with cured foam or utilize undesirable solvent to obtain the required and desired operating time.
Recent approaches have incorporated the concept of keeping the flow of plural polyurethane foam components separate within the dispenser until the streams enter a separate mixing chamber to prevent the reactive impingement mixing of the foam components from occurring within the dispenser and clogging the internal flow passages within the apparatus with cured or set foam. U.S. Pat. No. 4,913,317 discloses one apparatus that has taken such an approach with the use of a central plug. However, this approach still has the potential for clogging since it uses a compressed gas purge that has proven ineffective in the past to prevent the buildup of foam without the use of a solvent.
Additionally the use of an aqueous medium to flush a dispensing apparatus heretofore has not been successful because residual water reacts with the isocyanate component and damages the unit.
These problems are solved in the design of the present invention by providing an improved insert within a plural component dispensing apparatus that serves to separate the flow streams of plural urethane foam components and permits the flow of water through separate ports in the insert to flush from the dispensing apparatus any residual components or reacted components that have formed urethane foam.